Microfilm coding method and apparatus

ABSTRACT

A microfilming apparatus wherein one of two transparent plates which define the image plane for originals carries a row of enclosed electric lamps serving to encode information on microfilm during exposure of successive originals onto successive microfilm frames. The encoded information facilitates the finding of selected microfilm frames. The plates are movable from operative to exposed positions to be accessible for cleaning. The number and distribution of lamps which light up to encode information on microfilm is controlled by a programming unit which can be actuted by hand or automatically, either in response to detection of successive originals in the image plane or in response to detection of signal generating sheets which are fed into the image plane alternately with successive originals. A detector scans the thickness and/or the conductivity of signal generating sheets and causes the programming unit to change the number and/or distribution of lamps which are lighted simultaneously or substantially simultaneously with the exposure of successive originals onto the microfilm.

United States Patent 1 Pfeifer et al.

[ MICROFILM CODING METHOD AND APPARATUS [75] Inventors: Josef Pfeifer, Unterhaching; Wilfried Hofmann; Karl-Heinz Dietrich, both of Munich, all of Germany [73] Assignee: Agfa-Gevaert Aktiengesellschaft,

Leverkusen, Germany 22 Filed: Apr. 12, 1972 211 Appl. No.: 243,201

[30] Foreign Application Priority Data Apr. l7, l97l Germany P 21 18 732.6 Dec. 4, i971 Germany P 2l 60 211.9

[52] US. Cl. 95/l.l, 355/40 [51} Int. Cl. G03b 17/24 [58] Field of Search 95/l.l; 355/40 [56] References Cited UNlTED STATES PATENTS 3,202,045 8/l965 Arsenault et al. 355/40 X 3,334,539 8/1967 Kleist et al 355/40 [451 Aug. 7, 1973 Primary ExaminerJohn M. Horan Att0rneyMichael S. Striker {57] ABSTRACT A microfilming apparatus wherein one of two transparent plates which define the image plane for originals carries a row of enclosed electric lamps serving to encode information on microfilm during exposure of successive originals onto successive microfilm frames. The encoded information facilitates the finding of selected microfilm frames. The plates are movable from operative to exposed positions to be accessible for cleaning. The number and distribution of lamps which light up to encode information on microfilm is controlled by a programming unit which can be aetuted by hand or automatically, either in response to detection of successive originals in the image plane or in response to de tection of signal generating sheets which are fed into the image plane alternately with successive Originals. A detector scans the thickness and/or the conductivity of signal generating sheets and causes the programming unit to change the number and/or distribution of lamps which are lighted simultaneously or substantially simultaneously with the exposure of successive originals onto the microfilm.

11 Claims, 6 Drawing Figures MICROFILM CODING METHOD AND APPARATUS BACKGROUND OF THE INVENTION The present invention relates to microfilming apparatus in general, and more particularly to improvements in a method and apparatus for encoding indicia on microfilm simultaneously with exposure of successive originals onto recessive microfilm frames. Still more particularly, the invention relates to improvements in a method and apparatus for exposing on microfilm indicia which serve to facilitate rapid and convenient finding of selected microfilm frames for observation in a microfilm reading or microimage retrieving apparatus.

It is already known to provide a microfilm with characteristic indications which facilitate the finding of desired frames or groups of frames. As a rule, the indications are in the form of black lines or strips (edge cod ing or line coding)'which are exposed onto microfilm between successive frames. The number and/or the distance of lines from a marginal portion or edge of the film is indicative ofa particular microimage or ofa particular group of microimages. The means for producing the lines includes white levers which are adjustable in or close to the image plane so as to provide a desired number of combinations. The levers must be moved by hand so as to be located at a desired distance from the edge of microfilm and/or from each other. The image of each lever appears as a black line or strip. The exposure of a selected group of levers to light takes place simultaneously with the exposure of the thus identified originalor group of originals. The microfilm reading or microimage retrieving apparatus is provided with means for allowing an observation of the black lines or strips on microfilm to facilitate rapid placing of a selected frame or group of frames into a position for proj'ection of the information onto a screen or the like.

A drawback of presently known coding apparatus is that the aforementioned white levers are immediately adjacent to the image plane in which the originals are transported for the exposure of their images onto microfilm. The originals are guided between two light transmitting plates which are fixedly mounted in the housing of the apparatus. The levers and the plates are likely to be contaminated so that they require frequent inspection and cleaning. Such procedure is tedious and time-consuming because the guide plates and the levers are not readily accessible.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved method of encoding frame identifying indicia on microfilm.

Another object of the invention is to provide a method according to which the selection of the number and/or distribution of identifying indicia can be carried out manually or automatically.

A further object oftheinvention is to provide a novel and improved indicia applying or coding apparatus which dispenses with manually movable levers and affords convenient access to the parts which are likely to require frequent inspection due to contamination or for other reasons.

An additional object ofthe invention is to provide the apparatus with novel means for initiating the exposure of identifying indicia onto microfilm and with novel means for automatically changing the number and/or distribution or orientation of such indicia in response to completed exposure ofsuccessive originals or groups of originals onto microfilm.

Still another object of the invention is to provide the apparatus with novel means for mounting the guiding devices for originals.

A feature of the invention resides in the provision of a method of coding microfilms simultaneously with exposure of originals onto successive microfilm frames. The method comprises the steps of placing sheets of originals into an image plane alternately with second sheets which differ from the originals in at least one detectable characteristic, positioning a plurality of electric lamps or analogous light sources in the region of the image plane, scanning the image plane and generating signals (preferably electric signals) in response to detection of second sheets, and utilizing the thus generated signals to image onto microfilm different groups of light sources whereby the images of selected light sources constitute on the microfilm encoded information (which can be located in the frame lines between successive microfilm frames) identifying the images of originals adjacent tothose second sheets whose detection triggered the generation of respective signals.

The detectable characteristic of the second sheets may be their thickness and/or their ability to conduct electric current. i

The method may further comprise the steps of stacking the original sheets and the second sheets so that the original sheets of the resulting stack alternate with sec- 0nd sheets, and feeding successive sheets of the stack into and advancing them in the image plane.

The signals may be produced in response to completion of an electric circuit by means of a selector switch having a preferably movable portion which extends into or is immediately adjacent to the image plane. The circuit may form part of a programming unit which automatically changes the number and/or distribution or sequence of those light sources which are to be imaged onto microfilm in response to generation of successive signals.

The light sources may be arranged in at least one row which preferably extends transversely of the direction of movement of original and second sheets in the image plane, and the light sources are preferably confined in a suitable enclosure to protect them against contamination by dust or other foreign matter.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved coding apparatus it self, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. I is a fragmentary perspective view of a microfilm coding apparatus which embodies one form of the invention; I

FIG. 2 is a fragmentary vertical sectional view of a second apparatus;

FIG. 3 is an enlarged view of a detail in FIG. 2, showing a selector switch in the open position;

FIG. 4 illustrates the structure of FIG. 3; but with the selector switch in closed position;

FIG. illustrates a modified selector switch in open position; and

FIG. 6 illustrates the selector switch of FIG 5 in closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring first to FIG. 1, there is shown a portion of a microfilm coding apparatus which embodies one form of the invention. The apparatus comprises a housing 1] which accommodates a customary projection lens, a light source, a platform which maintains successive frames of microfilm MF in the focal plane of the lens and other customary components which are not shown in the drawing. The microfilm MF can be paid out by a supply reel SR and collected by a takeup reel TR so that a portion thereof extends across the optical axis of the lens and receives images of successive originals one of which is shown in FIG. I, as at 1. This original is located in an image plane 3 extending between two light transmitting guide plates 5,6. The plates 5,6 extend transversely of the direction of transport (arrow A) of successive originals l in the image plane 3. The transporting mechanism for originals 1 comprises two driven advancing rolls 4 located at the opposite sides of the image plane 3 upstream of the guide plates 5,6, and two similarly mounted advancing rolls 2 located downstream of the guide plates.

The guide plate 6 carries an elongated casing or enclosure 8 for at least one row of light sources here shown as electric lamps 7. The lamps 7 are equidistant from each other and they serve to expose coding lines or strips on the microfilm MF. Such strips can be exposed on the frame lines between successive frames F of the microfilm MP. The circuit of one or more lamps 7 can be completed by a programming unit 17 and the images of selected lamps are encoded in the form of strips or lines on microfilm MF which moves in the focal plane of the lens. The selected lamp or lamps 7 will be imaged on microfilm MF only during the interval when they are not overlapped by an original I. The exposed strips or lines are parallel to the edges of microfilm MF which latter moves in synchronism with the originals l in a manner well known in the art of continuous microfilming systems. The number of coding lines, their distance from each other and their distance from the edges of microfilm MF are indicative of the respective film frames.

The guide plates 5,6 are secured to each other at one end, as at 5b, and are mounted on a carrier lever 9 which is turnable on a shaft 10. The shaft 10 is located without the image plane 3 and is mounted in a portion of the housing 11. The other ends of the guide plates 5,6 are connected to each other by a U-shaped handle 12 having two elastic prongs or arms 12!) and provided with a pair of coaxial detent pins 12a which can enter complementary recesses or openings 13a provided in the arms of a U-shaped bracket 13 which is mounted in the housing 11. Prior to pivoting of the guide plates 5,6 to an open or exposed position (arrow 14), the operator grips the prongs 12b of the handle 12 and moves the prongs toward each other to thereby withdraw the detent pins 120 from the respective openings 13a. The

' plates 5,6 are then free to turn about the axis of the shaft 10 to a position of accessibility for the purposes of inspection and/or cleaning. The lamps 7 are confined in their casing 8 so that they are protected from dust or other foreign matter. The conductors which serve to connect the lamps 7 with a source of electrical energy form a flexible cable 15 which extends lengthwise through the casing 8 and one end of which carries a plug 16 with a requisite number of male contacts which can engage female contacts in a socket 16a of the programming unit 17.

All details of the programming unit 17 form no part of the present invention. This unit comprises an assembly which can complete the circuits of lamps 7 in the casing 8 in a desired sequence so that each of a series of successively photographed originals I is identified by a different combination and/or different number of coding lines constituting the images of selected lamps 7. The unit 17 comprises adjustable decimal counters 17a which can complete the circuits of selected lamps 7. Each counter 17a has a window to expose a digit of a counter wheel and can be adjusted by a pushbutton 171) which can be depressed by hand to select the observable digit and to thus determine the number and/or distribution of lamps 7 whose circuits are about to be completed. The illustrated programmingunit 17 with three adjustable counter wheels can select different groups of one, two or three lamps 7 which, with a total number of, for example, thirty lamps in the casing 8, can provide an extremely large number of different combinations of coding lines.

A sequence selecting pushbutton of the programming unit 17 is actuatable by hand to adjust the counters 17a ina predetermined sequence without necessitating any actuation of the individual pushbuttons 17b. Thus, all the operator has to do is to press the button 17c upon completed imaging of an original I whereby the programming unit 17 automatically selects the next one of a predetermined sequence of lamp groupings. The pushbutton 17c controls a sequence selector switch which is connected in parallel with a normally open auxiliary sequence selector switch l9 by means of a flexible remote control cable 18. The switch l9 can be closed by hand, by a foot pedal or automatically in response to completed transport of an original 1 beyond the advancing rolls 2. For example, the coding apparatus may be equipped with a conventional photoelectric detector (not shown) which scans the path of originals l in the image plane 3 and automatically closes the switch l9 (or the switch'which is actuatedby the pushbutton 17c) in response to detection or completed passage of an original.

The casing of the programming unit 17 further contains a signal generating'device 20 which produces a visible or audible signal in response to actuation of the pushbutton 17c or auxiliary selector switch 19 to thus inform the operator that the selection of a different group oflamps 7 has been completed. The signal generating device 20 can also serve to warn the operator that a new lamp selection must take place prior to transport of the next original 1 past the optical system.

A further switch 17d serves to activate or deactivate the entire programming unit 17. The latter is preferably mounted in or on or adjacent to the housing 11 so as to be readily accessible to the operator.

It is clear that the microfilm coding apparatus of FIG. 1 is susceptible of many additional modifications. For example, the programming unit 17 can be used in a duplex microfilming apparatus. Furthermore, the guide plates 5,6 can be mounted on the member 5b and/or on the handle 12 for pivotal movement with respect to each other. Still further, the axis of the shaft l can be placed into the image plane 3 provided that the plates 5,6 are still movable between the illustrated operative positions and exposed positions in which they can be readily inspected and/or cleaned, i.e., that such movements of the plates are not impeded by the advancing elements 2,4 and/or other components of the apparatus. The arrangement is preferably such that the parts 5, 6, 5b, 9 and a sleeve 9a of the part 9 can be liftedoff the shaft 10 after the plates 5,6 are moved to their exposed positions. This allows for rapid replacement of the entire assembly including the parts 5-9, 9a, l2, 15, 16, 5b with a similar assembly. The lamps 7 can be replaced with other types of encoding means as long as the selected encoding means are capable of coding the microfilm in a readily detectable manner and in such a way that the encoded information can be readily discerned and processed for rapid seleection of a desired microfilm frame F.

The auxiliary switch 19 can be connected in parallel with one or more additional auxiliary sequence selector switches which are suitably distributed so that the selection of successive groups of lamps 7 can be made at which monitors the originals for the presence of specialmarkers serving to trigger a change in the setting of counters 17a in the same way as if the operator were to actuate the pushbutton 17c or auxiliary switch 19.

If several originals I are assembled into groups which are exposed onto successive frames of a roll of microfilm, each such group of originals can be identified by a single set of coding lines. If the groups of originals or discrete originals are properly stacked or otherwise prepared for transport past the optical system in a predetermined sequence, the operator will actuate the pushbutton 170 or the switch 19. The pushbuttons 17b serve to select any desired grouping of lamps 7 for any desired original.- The main purpose of the signal generating device 20 is to insure that the operator will not re-. peatedly actuate the pushbuttom 170 or the switch 19 prior to introduction of the next original or group of originals into the image plane. This could'result in improper coding of successive microfilm frames. 7

' The casing 8 can accommodate two or more rows of electric lamps 7'or analogous light sources. If the lamps 7 form two or more rows, the lamps of each row may be staggered with respect to the lamps of the other row 01' rows.

FIGS. 2 to 4illustrate a portion ofa second microfilm coding apparatus wherein all' such parts which are clearly analogous to or identical with the corresponding parts of the first apparatus are denoted by similar reference characters. The housing] l-accommodates a receptacle or tray llafor a stack of originals lwhich alternate with signal generating sheets 30 of conductive material. A platform 11b in the tray llais biased upwardly by helical springs 11c so that the uppermost original l'or sheet 30bears against the periphery of an elastic feeding roll 22which is driven continuously or intermittendly to introduce successive originals 1 and sheets 30 into theimage plane 3. Such image plane is adjacent to the upper side of a table 23 whichguides successive originals l and sheets 30 into the nip between the advancing rolls 4. From there on, such originals and sheets advance through the gap between the guide plates 5,6 (above the casing 8 for the lamps 7) and into the range of advancing rolls 2 which transport the originals and sheets to a further destination (arrow A). The casing 8 extends transversely of the direction of movement of originals I and sheets 30 in the image plane 3. The manner in which the programming unit 17 can complete circuits of selected lamps 7 in a given sequence or at the will of the operator (see the pushbuttons 17b) is the same as described in connection with FIG. 1.

The apparatus of FIGS. 2 to 4 further comprises a modified sequence selector switch which replaces the auxiliary switch 19 of FIG. 1. The modified selector switch comprises a fixed contact which constitutes the table 23 and a movable contact 28 here shown as a lever which is mounted in the housing 11 on a pivot pin 280. The movable contact or lever 28 is connected with the programming unit 17 by a first conductor 29 which is soldered to the pivot pin 28c, as at 29b, and the table 23 is connected with the unit 17 by a second conductor 29a. Thus, the switch including the parts 23 and 28 can complete an electric circuit when the current is free to flow between the tip of the lever 28 and the table 23. In order to prevent the closing of this switch when the table 23 does not support a sheet 30, the table 23 is providedwith an insert 23a ofinsulating material which is contacted by the lever 28 in the absence of a sheet 30 or an original I on the table. The originals l are not conductive so that the switch 23, 28 cannot complete an electric circuitof the programming unit 17 when the table 23 supports an original. However, the sheets 30 conduct current and, therefore, whenever a sheet 30 moves into the space below the tip of the lever 28, current can flow between the conductors 29, 29a and the programming unit 17 automatically changes the grouping of lamps 7 whichare to be imaged'onto microfilm in conjunction with the next-following original 1. The table 23 may consist of sheet metal and at least a portion of the pin 28c conducts current so that the lever 28 is electrically connectedwith the programming unit 17 by way of the conductor 29.

It will be noted that the selector switch including the parts 23, 28 will coinplete a circuit inthe programming unit 17 whenever the feeding roll 22 introduces a signal generating sheet 30 into the nip between the advancing rolls 4. FIGQ3 sh'ows the'selector switch 23, 28 in inoperative position because the table 23 supports an original l; In FIG. the selector switch is closed because a sheet 30 on the table 23'contacts the lever 28.

FIGS. 5 and'6 illustrate a portion of an apparatus with a selector'switch which constitutes a modification ofthe switch 23, 28'shown in FIGS. 3 and 4. The stack on the platform lla (not shown in FIGS. Sand 6) con sists of alternating information-bearing originals l and relatively thick signal generating sheets 30' whose thickness may be a multiple of the thickness of a sheet 30 or an original 1'. The modified selector'switch comprises a first elastic contact 29' which corresponds to the conductor 29a of FIGS. 2-4, a second elastic contact 29a which corresponds to the conductor 29 of FIGS. 2 4,- and a two-armed lever 28' which is pivotable on a pin 28c and need not be made of currentconducting material. The lower arm of the lever 28' carries a roller follower 28b which is biased against the upper side of a non-conductive table 123 by the elastic contact 29a and/or by a discrete spring (not shown). The other arm 28a of the lever 28' is adjacent to the contact 29a and can move this contact against the contact 29' in response to travel of sheet 30' along the upper side of the table 123 (see FIG. 6). When the roller follower 28b abuts against the table 123 or against an original 1 (see FIG. the arm 28a cannot close the contacts 29, 29a so that the programming unit 17 receives an impulse to change the grouping of lamps 7 only when the roller follower 28b engages a sheet 30. An advantage of the apparatus whose parts are shown in FIGS. 5-6 is that accidental closing of the selector switch 29, 29a, 28' is much less likely than in the apparatus of FIGS. 2-4 and that the sheets 30' need not consist of current-conducting material. An advantage of the apparatus of FIGS. 2-4 is that a full stack on the platform 11a in the housing 11 can comprise a large number of originals 1 because the thickness of signal generating sheets 30 need not exceed and can be less than that of the originals l. The sheets 30 may consist of metallic foil.

It is clear that the lower arm of the lever 28 can be suitably rounded so that the roller follower 28b can be dispensed with. It is also possible to mount a roller follower on the lever 28 of FIGS. 2-4, provided that the roller follower can conduct current between a sheet 30 and the lever 28.

The selector switch need not be mounted upstream of the advancing rolls 4. For example, at least certain parts of such selector switch can be mounted between the rolls 4 and the guide plates 5,6, immediately behind the guide plates 5,6 or even behind the advancing rolls 2. Furthermore, the coding apparatus can employ other types of selector switches which are actuatable as a function of the conductivity, thickness and/or other detectable characteristics of the material which is being transported in the image plane. The apparatus of FIGS. 2-4 or 5-6 can be simplified if the originals l and sheets 30 or 30' are fed by hand. However, the automatic feeding of such sheet-like material has been found to result in substantial savings in time and is more reliable than if the control of the selector switch or switches is entrusted to the attendants. Furthermore, a single attendant can service two or more microfilm coding apparatus since'all that is necessary is to insure that each apparatus contains a supply of microfilm and a stack of alternating originals 1 and sheets 30 or 30'. It is also within the purview of the invention to mount the selector switches of FIGS. 3-4 and 5-6 in a single apparatus whereby the switch of FIGS. 3-4 is inactive when the stack on the platform 11a contains sheets 30' (which need not be conductive), and the switch of FIGS. 5-6 is inactive when the stack contains sheets 30 (whose thickness need not exceed the thickness of an original). Finally, it is also possible to modify the selector switch of FIGS. 5-6 in such a way that it completes a circuit in response to detection of sheets whose thickness is less than the thickness of an original.

Without futher analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended.

We claim:

1. A method of coding moving microfilms alternatively with exposing of moving sheet-like originals, comprising the steps of placing sheet-like originals into an image plane alternately with second sheets which differ from the originals in at least one detectable characteristic and moving said alternating originals and second sheets in said image plane in a predetermined direction; imaging successive originals onto successive frames of moving microfilm; positioning at least one row of light sources transversely of the direction of movement of said originals and second sheets in said image plane; scanning said image plane and generating signals in response to detection of said second sheets; and utilizing said signals to image different groups of said light sources onto moving microfilm whereby the images of selected light sources constitute on moving microfilm encoded information identifying the images of originals adjacent to those second sheets whose detection triggered the generation of the respective signals and the thus encoded information alternates with the images of said originals.

2. A method as defined in claim 1, wherein said detectable characteristic of said second sheets is their ability to conduct electric current.

3. A method as defined in claim 1, wherein said detectable characteristic is the thickness of said second sheets.

4. A method as defined in claim 1, further comprising the steps of stacking said original sheets and said second sheets so that the original sheets of the resulting stack alternate with second sheets, and feeding successive sheets of said stack into said image plane.

5. A method as defined in claim I, wherein said signals are electric signals which are produced in response to completion of an electric circuit by means of a switch, a portion of which extends into said image plane.

6. A method as defined in claim 1, further comprising the step of confining said light sources in an enclosure against contamination by dust or other foreign matter.

7. Apparatus for coding moving microfilm altematingly with exposing of moving originals onto successive microfilm frames, comprising guide means'defining an image plane for successive sheet-like originals; means for feeding into said image plane successive originals alternatingly with second sheets each of which has at least one readily detectable characteristic; means for transporting said alternating originals and second sheets in said image plane in a predetermined direction; at least one row of light sources adjacent to said image plane and extending transversely of said direction, said light sources being operable to emit light and to be thereby imaged onto moving microfilm whereby the images of light sources constitute on microfilm encoded information identifying the adjacent images of originals; programming means actuatable to select the light sources which are operated to identify the images of successive originals; and detector means arranged to produce signals for actuation of said programming means in response to detection of successive second sheets in said image plane.

8. Apparatus as defined in claim 7, wherein said detector means comprises a normally open selector switch which is closed on contact with successive second sheets.

9. Apparatus as defined in claim 8, wherein said characteristic of said second sheets is their ability to conduct electric current and said switch comprises a first contact adjacent to one side of said image plane and a second contact adjacent to the other side of said image plane and being electrically connected with said first contact when said contacts simultaneously engage a second sheet.

10. Apparatus as defined in claim 8, wherein said characteristic is the thickness of said second sheets and sheets. 

1. A method of coding moving microfilms alternatively with exposing of moving sheet-like originals, comprising the steps of placing sheet-like originals into an image plane alternately with second sheets which differ from the originals in at least one detectable characteristic and moving said alternating originals and second sheets in said image plane in a predetermined direction; imaging successive originals onto successive frames of moving microfilm; positioning at least one row of light sources transversely of the direction of movement of said originals and second sheets in said image plane; scanning said image plane and generating signals in response to detection of said second sheets; and utilizing said signals to image different groups of said light sources onto moving microfilm whereby the images of selected light sources constitute on moving microfilm encoded information identifying the images of originals adjacent to those second sheets whose detection triggered the generation of the respective signals and the thus encoded information alternates with the images of said originals.
 2. A method as defined in claim 1, wherein said detectable characteristic of said second sheets is their ability to conduct electric current.
 3. A method as defined in claim 1, wherein said detectable characteristic is the thickness of said second sheets.
 4. A method as defined in claim 1, further comprising the steps of stacking said original sheets and said second sheets so that tHe original sheets of the resulting stack alternate with second sheets, and feeding successive sheets of said stack into said image plane.
 5. A method as defined in claim 1, wherein said signals are electric signals which are produced in response to completion of an electric circuit by means of a switch, a portion of which extends into said image plane.
 6. A method as defined in claim 1, further comprising the step of confining said light sources in an enclosure against contamination by dust or other foreign matter.
 7. Apparatus for coding moving microfilm alternatingly with exposing of moving originals onto successive microfilm frames, comprising guide means defining an image plane for successive sheet-like originals; means for feeding into said image plane successive originals alternatingly with second sheets each of which has at least one readily detectable characteristic; means for transporting said alternating originals and second sheets in said image plane in a predetermined direction; at least one row of light sources adjacent to said image plane and extending transversely of said direction, said light sources being operable to emit light and to be thereby imaged onto moving microfilm whereby the images of light sources constitute on microfilm encoded information identifying the adjacent images of originals; programming means actuatable to select the light sources which are operated to identify the images of successive originals; and detector means arranged to produce signals for actuation of said programming means in response to detection of successive second sheets in said image plane.
 8. Apparatus as defined in claim 7, wherein said detector means comprises a normally open selector switch which is closed on contact with successive second sheets.
 9. Apparatus as defined in claim 8, wherein said characteristic of said second sheets is their ability to conduct electric current and said switch comprises a first contact adjacent to one side of said image plane and a second contact adjacent to the other side of said image plane and being electrically connected with said first contact when said contacts simultaneously engage a second sheet.
 10. Apparatus as defined in claim 8, wherein said characteristic is the thickness of said second sheets and said switch further comprises follower means arranged to track successive sheets in said plane and to close said switch in response to engagement with successive second sheets.
 11. Apparatus as defined in claim 10, wherein said follower means is a pivotable lever and the thickness of said second sheets differs from the thickness of said original sheets so that said lever respectively assumes first and second angular positions in response to engagement with said original sheets and said second sheets. 